Literally the first thing on wikipedia:
The cubit is an ancient unit of length based on the distance from the elbow to the tip of the middle finger.
I'm pretty sure the dude is trying to say that the measurement is not accurate. I'm not surprised that it could be accurate and standartized from one town to the next. As soon as the first dissagreement starts, it's gonna get standartized. Otherwise it's useless as unit.
Meter has a bonus that it doesn't allow people to use his body parts for almost precise measurement. Actually blocks a lot of retards from saying "Nuh uh, I myself measured it, so I'm right and your ruler is wrong!"
Now when I think of it, Cubit is more or less exactly like the inch. It doesn't match basically anyones finger, different countries had their own standard. You can and many people do use it as a measurement. Side-effect, seeing memes about Napoleon being a dwarf. XD